With the advancement in network environments, service providers begin to release a service of pushing contents to a user.
Particularly, the service providers actively plan to provide a service of previously pushing (downloading) multimedia contents into a mobile terminal of a user subscribing the service and allow the user to play back the previously downloaded contents even in an offline state or in a situation difficult to receive a streaming service.
A technique of minimizing network use cost is required to provide a service of downloading multimedia contents of a large volume, and a method utilizing a content delivery network (CDN) is widely used.
The CDN is a system for installing a plurality of cache servers (temporary storage devices) under the network of an Internet service provider (ISP), moving contents provided by a contents provider (CP) in advance, and downloading the contents in response to a demand of a user, which is a technique capable of improving transmission speed and preventing degradation of speed and loss of data that can be generated in the middle of transmitting data by moving the contents to a location near the user in advance through the CDN.
It is required to develop a contents transmission technique capable of safely and speedily processing traffic which is concentrated when multimedia contents of a large volume are transmitted.
In addition to this, a technique of encoding multimedia contents which will be transmitted is required in order to safely transmit the contents to a user terminal. Particularly, standardized image compression techniques such as Moving Picture Experts Group 2 (MPEG-2), MPEG-4, H.264 and the like are generally used.
An image compression method based on block matching among the standardized image compression techniques is a compression method which removes temporal redundancy between blocks using a motion estimation method.
The block matching is a process of dividing each frame of an image into blocks and searching for a block matching to a block of a currently encoded/decoded frame from previous frames or previously encoded/decoded frames, and the image compression method based on block matching is a method of compressing and transmitting an image using a difference between the matching blocks searched through the block matching.
Particularly, a method of searching for a matching block based on motion estimation may estimate a region in which an error value between the current block and the previous block, such as Sum of Absolute Difference (SAD) or Sum of Square Difference (SSD), is minimized as a block matching to the current block, and may calculate a difference between coordinates of matching blocks as a motion vector and use the difference in image compression.
In order to determine block matching based on the motion estimation, the SAD or the SSD needs to be calculated for all pixels in a motion search region.
For example, if a block size is N×N pixels and a motion search region is 32×32, 1024*(2N×N−1) times of addition/subtraction operations are required, and if the image size about 100N×80N, 8192000*(2N×N−1)*(N×N) times of operations are required.
The quantity of operation used for such block matching is as large as to occupy 50% of the quantity of operation used for encoding in maximum, and thus system load is induced, and processing speed is delayed.
That is, it needs to develop a contents transmission technique capable of safely and speedily processing traffic concentrated when large-volume multimedia contents are transmitted and a block matching technique capable of reducing the operation quantity.